One factor could be the power levels. If the fanfiction writer wants to boost Naruto's power in a new and different way, they might draw inspiration from Kaygua's power characteristics. So Naruto ends up with some traits that make him seem like Kaygua.
Well, in fanfiction, Naruto could be made to be like Kaygua. One similarity could be their combat styles. Maybe in the fanfic, Naruto adopts a more brutal and direct combat style similar to what Kaygua might have. Also, their backstories could be made alike in some ways. Both could be presented as having a difficult past that shapes their present personalities. However, this is all very much dependent on the creativity of the fanfiction writer.
The heroic deeds of the characters. Just like knights, Naruto and his friends perform brave acts to protect their village. And the love stories, like Naruto's love for Hinata, are like the romances knights might have in a castle setting.
Well, perhaps someone who is not very familiar with both might misinterpret some elements. But in reality, Naruto's ninja - based powers, such as chakra control and jutsu usage, are very different from shigigami - related concepts. Naruto's story is centered around the ninja world, its clans, and the pursuit of power and peace within that world, while shigigami has its own distinct characteristics that don't match up with Naruto at all.
The unpredictable plot. One minute Percy could be at Camp Half - Blood training, and the next he's thrown into a life - threatening quest. That's chaos.
The use of Greek mythology makes it seem so. It's like taking the old and making it new. Just as fanfiction does with existing works.
The backstories. The Marauders' backstories are so rich and intertwined with Harry's world. For example, Remus Lupin being a werewolf and his relationship with the other Marauders. Also, the fact that Harry inherits the Marauders' Map. All these things create a connection that gives it a fanfiction - like feel.
The new power - ups like Ultra Instinct make it seem like fanfiction. They are so extreme compared to the original power levels in Dragon Ball. It's like something a fan would dream up to make the battles even more epic.
The supernatural elements. Just like in the Mikealsons' story, Bella Swan is in a world filled with vampires and other supernatural beings in the Twilight series. This similarity in the presence of the supernatural could make her seem like she could be part of a Mikealsons fanfiction.
The setting. Hogwarts is a school for wizards, which is similar to the types of institutions often found in mage fanfiction. It's a place where young magic - users learn and develop their skills. Also, the existence of a hidden magical world parallel to the Muggle world is a common trope in mage - related fictional works.
The character relationships and growth can seem fanfiction - like. Some characters get sudden changes in their personalities or abilities without a clear explanation. In fan - made stories, this can happen due to the writer's desire to quickly move the story along or create a new dynamic. In 'Dragon Ball Super', we see this with characters like Goku, who sometimes has a rather simplistic view of things that doesn't always seem in line with his previous character development.